The invention relates in general to power demand control for switching electrical loads according to a priority schedule and more particularly to a power demand control system featuring cell line control, in an electrochemical plant facility supplied with energy from the utility company, so as to keep the demand at the end of a period of control within a preassigned demand limit while maximizing plant production.
Power demand control is known in which loads are controlled in accordance with a priority schedule which is changed, or fixed, in accordance with the dynamics of current consuming production units and of sheddable loads. Adaptive load priority determination with a power demand control system is generally known from U.S. Pat. No. 4,204,127, issued May 20, 1980. The system and method disclosed in the aforementioned patent application have been described in the context of an arc furnace installation, since in such installations the decision to switch, or not to switch, should not only take into account the requirements of power demand limit but also the economics and requirements of production. For the purpose of the present description, U.S. Pat. No. 4,204,127 is hereby incorporated by reference.
This invention is directly applicable to a computerized control system for the heavy chemical industries which are using an electrolysis process, such as the chlor-alkali industries. Thus, chlorine and caustic soda are produced almost entirely by electrolytic methods from fused chlorides, or aqueous solutions of alkali metal chlorides. In such a plant the energy consumed by the electrolyzer cells represents the large majority of the overall energy consumption from the utility company power line. The energy consumed in the electrolysis of the brine is the product of the current flowing and the potential of the cell. The load factor, e.g. the ratio average to maximum demand is high, namely of the order of 94% to 96%. Despite such a high load factor, any increase by a few percentages, say up to 98 or 99%, represents a sizable yearly profit increase to the manufacturer.
Accordingly, an object of the present invention is to provide a power demand control system which, besides some sheddable and reconnectable loads, operates mainly on electrolytic cells which can be controlled so as to maximize productivity without exceeding a power demand limit.
Another object of the present invention is to provide, in accordance with a priority schedule, for mininal switching and adjusting of loads mainly including electrolytic cells while closely meeting a power demand limit not to be exceeded at the end of any of successive demand periods.
A further object of the present invention is to control with a computer, during a given demand period, the power rate of a plurality of electrolytic cells in an electrolytic plant in order to attain an ideal rate of consumption before the subsequent demand period, thereby to minimize switching and adjusting of loads under the constraint of an assigned power demand limit.
Still another object of the present invention is to maximize the production from electrolytic cells in a chemical plant by cell selection and cell adjustment while minimizing the selection and adjustment control steps, and maintaining each cell between a maximum and a minimum amperage.